LSS POWER TUBE PROBLEMS.....RED HOT POWER TUBES

[hippdogs]

I have an LSS head, still under warranty. I was practicing yesterday and got a distortion and sudden loss of power. Having read my manual, I turned on the stand-by, turned the head around and saw that the two EL-84's on the left (closest to the rectifier tube) were glowing red hot. I turned off the amp, located my trusty new matched pair of replacement tubes, then went to my dealer and got a second set of new tubes, and installed all four of them, 2 blues, 2 yellows (bought at different times)....everything worked perfectly.....for 24 hours....then suddenly, the same problem, except this time the tubes that were glowing red hot were the far right pair of tubes, furthest from the recto tube.

HELP!

 

[Mork]

That's odd, because the tubes are paired as middle pair and outside pair... What power setting were you switched to?

 

[hippdogs]

Tell me about it.....both channels set on the 30 watt setting. If I recall.....all 4 el-84's for the 30 watt, ouside el-84's for the 15 watt, and the furthest away (right) from the recto tube is the 5 watt el-84? :roll:

 

[BobL]

Hippdogs,
This is not an uncommen problem with EL-84's and I have run into the same problem more than once myself. This leads to another issue, one with Mesa, and that being they won't talk to you unless the tubes are a matched quad, AND they are Mesa tubes. Your best bet is to buy a matched quad of EL-84's and replace all of the power tubes at the same time.

You stated that you replaced the defective pair, the pair with the runaway plates. That would work fine if they were a match for the other tubes, AND you can be 100% positive the remaining tubes were not damaged. I have always, for over 45 years, replaced tubes as a set, and I think you'll find that if no damage has been done to the amp replacing your output tubes as a set will be the cure especially with EL-84s.

 

[hippdogs]

Mesa got back to me by phone on this. Their recommendation is to move the tubes around and try to identify which tube is causing the problem. I was able to locate the little bast#@d and all is good once again. Bad New Tube! Luckily, the EL-84's are not that expensive and my dealer cuts me some slack on the cost of the tubes cause they LOVE me. Mesa said not to worry about matched sets so much. 8)